Pension Plan and Other Postretirement Benefits (Pension and Other Postretirement Benefit Costs) (Details) - Pension - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 2
Interest cost	1	1
Expected return on plan assets	(1)	(2)
Amortization of prior service cost	0	0
Amortization of net loss	0	1
Net periodic benefit cost	$ 2	$ 2